American plum trees grow best and produce the most fruit when pruned into a pyramid shape. Begin this process the first year you plant the whip of a tree in your garden. The pruning and shaping process continues for a total of three years. American plum trees are relatively pest- and disease-free. They will produce a small crop when they are about four years old and reach full production about six years after planting.
Pruning a Newly Planted Plum Tree
Prune a newly planted American plum tree by first cutting back the main stem so it is approximately two feet above the surface of the soil. Remove the topmost bud by rubbing it out with your fingers. There should be at least three and preferably four buds left on the “whip” that remains. (A “whip” is a newly-planted tree that has one upright stem and no branches.)
Prune as follows in June of the second year: Cut back the main central stem by about 18 inches to a point just above a bud. Beneath this there should be three or four additional new buds. Beneath these buds should be three or four branches that grew from the buds left on the “whip” when you pruned it the first year.
Prune the branches that grew during the tree’s first year during June of the second year after planting. Cut them back so they are approximately 10 inches long. Make the cut just above a healthy, outward-facing bud.
Prune in June of the third year as follows: Cut back the main central stem by about 18 inches to a point just above a bud. Beneath this there should be three or four additional new buds. Beneath these buds should be three or four branches that grew from the buds left when you pruned the tree in its second year. Beneath these branches will be the three or four branches that were left on the “whip” when you pruned during the tree’s first year.
Prune the branches that grew during the tree’s second year during June of the third year after planting. Cut them off so they are approximately 10 inches long. The tree will be structured as follows from the top down: 3 or 4 buds, 3 or 4 branches grown the second year, and cut back to 10 inches long this year, and 3 or 4 branches grown the first year that were cut back the second year but not this year.
Pruning Plum Trees that are 4 Years Old or Older
Prune mature plum trees in June. This includes any American plums that are four years old or older. First, remove broken, diseased or dead branches. Cut them off less than an inch from the main trunk using a downward facing cut. This will discourage water from collecting in the stub, which can invite disease or fungal infections.
Remove any branches that are crossing over or rubbing against any other branches. Rubbing branches can rip the bark which opens up the tree for disease or insects to take up residence.
Prune any branches that are growing toward the center of the tree. The object is to keep the center of the canopy open to allow sunlight to reach the leaves growing in the interior of the canopy as well as those growing at the outside of the canopy. This will increase the number of plums the tree produces.
Cut back side shoots growing from main branches so that only six leaves remain on them. (This encourages fruit to form the following year).
When the central or main stem reaches eight feet high, cut it back to 30- to 36-inches above the highest branch. This will keep your plum tree compact which will increase yields and make it easier to harvest.